This project will investigate the common neonatal stress mechanisms, hypoxia, hypothermia, and hyperosmotic feedings, on gastrointestinal hemodynamics in the neonatal (1 - 3 day old) piglet. Differentially labeled radioisotope microspheres, injected before and after the induced stress and/or stresses, will be used. The gut wall will be separated into layers and individually analyzed for isotope (sphere) content. These values, the mesenteric samples and a timed blood sample from the distal aorta, for calculation for a simultaneous cardiac output, will define central vs. peripheral blood flow changes. The labile neonatal piglet serves as the model for the premature neonatal human who develops necrotizing enterocolitis, a lethal ischemic bowel disease, when subjected to these stresses.